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Abstract:
The pupillary light reflex (PLR) regulates the amount of light entering the eye. It is driven by the activation of rods, cones, and intrinsically photosensitive ganglion cells (ipRGCs), with the latter expressing the melanopsin photopigment (λmax = 480 nm). The degree to which these different receptors contribute to the PLR and their relative temporal filtering properties are addressed in this study.
The temporal roll-off in pupillary response amplitude was measured using sinusoidally modulated stimuli at approximately logarithmically spaced temporal frequencies (0.01, 0.05, 0.1, 0.5, 1 and 2 Hz) displayed in the peripheral visual field (27.5° field size, central 5° blackened). The spectral composition of the stimuli was controlled with a device allowing for the construction of arbitrary spectral power distributions (OneLight Digital Light Engine). Modulations were directed at L and M cones (L+M) and melanopsin while silencing the other photopigment classes with the method of silent substitution. Two observers viewed the stimulus with their left eye pharmacologically dilated and with a 4.7 mm artificial pupil. The consensual pupillary response of their right eye was measured with an IR eye tracker (Cambridge Research Systems).
The amplitude of pupil response was measured for each modulation frequency and photopigment-directed stimulus. The resulting temporal transfer functions demonstrate different roll-off properties for L+M cone and melanopsin-directed stimulation. Specifically, L+M driven responses are temporally bandpass with maximal pupil modulation in response to 0.1 Hz stimulation, while melanopsin responses are temporally low-pass.
